1. Field of the Invention
The invention generally relates to novel nanocomposite hydrogels, and a method of preparing nanocomposite hydrogels, and more specifically to the application of nanocrystalline cellulose (NCC) as both crosslinker and reinforcement domain in polymer hydrogels. The approach relies on free radical polymerization to form the hydrogels using a variety of hydrophilic vinyl monomers. This invention is suitable for developing applications in medicine, engineering materials, sensors, and consumer products (e.g. highly absorbent hygiene products).
2. Description of the Prior Art
Polymer hydrogels are crosslinked hydrophilic polymer networks that swell when absorbing large amounts of water. Hydrogels have been investigated extensively in the past several decades for a large variety of applications, such as drug delivery, tissue engineering, stimuli-responsive sensor, etc.1-6 In general, hydrogels are soft and brittle. However, there are applications that require significant mechanical loads, for example, medical implants, and some electrochemical devices.7 Designing hydrogels for a multitude of novel and existing applications require them to possess sufficient mechanical strength, as well as retain their original properties, such as stimuli responsiveness and fast diffusion.
In nature, there are many hydrogels with very high mechanical strengths.7 Many marine plants, such as kelp, are polysaccharide hydrogels reinforced with polymeric or inorganic fibres. In the human body, cartilage, cornea, and the dermis are all fibre reinforced hydrogels. These fibres reinforce the hydrogels by acting as the load-bearing components.
Recently, three new hydrogels with good mechanical properties have been reported: topological gels, nanocomposite gels, and double network gels. The topological gels have figure-of-eight crosslinkers which are able to slide along the polymer chains.8 As a result, these gels are highly stretchable and can absorb large amounts of water. For nanocomposite gels, the polymer chains are crosslinked by nanoparticles, for instance, inorganic clay, instead of organic crosslinking agents.9 The nanocomposite hydrogels are also highly stretchable and have very good tensile strength. Double network hydrogels have two interpenetrating polymer networks: one is a highly crosslinked rigid polymer matrix, while the other one is a loosely crosslinked flexible polymer matrix.10 These double network hydrogels have very high hardness and toughness.